1. Field of the Invention
The present invention relates to a non-tracking solar collector device.
2. Description of the Related Art
Solar radiation collection devices incorporating reflector elements for focusing incident radiation onto an absorber element are well known. The reflector elements may consist of a large aperture elongated parabolic trough which moves to track the sun and thereby maintain the focusing of sunlight onto an absorber element. In the case where smaller aperture reflector troughs are used, a non-tracking stationary reflector may be used. Such reflectors are usually of the parabolic concentrator or compound parabolic concentrator (CPC) type.
The known non-tracking solar collector devices generally comprise a couple of reflector elements disposed on opposite sides of the absorber element.
The absorber element may constitute an elongated tube or a metal plate with attached metal tubes through which a heat transfer fluid is pumped for heat extraction. Alternatively an array of solar photovoltaic cells disposed on an elongated metal strip may be used for electricity production. To prevent overheating of the photovoltaic cells, the metal strip will generally have attached metal tubing through which a coolant fluid is pumped.
In the event that the absorber element may overheat, for example due to malfunction of the collector system resulting in the interruption of flow of the heat transfer fluid or coolant fluid, or when the fluid flow is temporarily interrupted for maintenance purposes, the reflector in a tracking system may be moved to a position which prevents solar radiation being focused onto the absorber element. In the case of non-tracking reflectors the absorber element is continuously illuminated by solar radiation, thus there is need for a simple mechanism to protect the absorber element from overheating.
Solar radiation collector devices incorporating non-tracking reflector troughs are usually arranged side-by-side to form a collector panel.
U.S. Pat. No. 3,162,189 describes a solar radiation collection device incorporating a parabolic dish reflector with a small boiler at the focus. Small blades interposed between boiler and reflector dish may be oriented to have minimal interference with light reflected from the parabolic dish toward the boiler, or by rotation of the blades through 90°, effectively interrupt the light reflected from the parabolic dish. The amount of energy incident on the boiler is determined by the orientation of the blades which is controlled by a thermometer attached to the boiler. The thermometer is of the enclosed liquid type and uses expansion of the liquid and vapor to expand a bellows which drives the rotation of the blades.
The rotating blade design is difficult to implement for a parabolic or compound parabolic trough reflector due to the elongated reflector and absorber element, the close proximity of the absorber element to the reflector surface in most non-tracking collector designs, and the wide range of directions for radiation incident on the absorber element after reflection from a trough reflector.
U.S. Pat. No. 4,475,536 describes a combined solar heat collector—skylight in which a plurality of reflector elements is translated by a short distance between a position which accomplishes heating of fixed absorber elements which are necessarily disposed below the reflector elements, and a position where the reflector elements channel light into the interior of the building, and also to intermediate positions where a combination of heating of absorber elements and illumination of the building interior can be obtained. Means for translation of the reflectors involves an electric motor controlled by a sensor which measures absorber temperature, and light intensity sensors in the interior of the building.
This translation mechanism is not specifically designed to prevent overheating of the absorber elements. Indeed this translation mechanism, involving translation of the entire reflector system, is very complex and in the case of large and elongated reflector elements does not quickly and efficiently control the sunlight intensity incident on the absorber element. Moreover, this translation mechanism is not suitable when the fixed absorber element is disposed between the reflector elements because translation of the reflector will be obstructed by the absorber element. Moreover, this translation mechanism requests a relatively large amount of applied force and energy for translating the reflector elements.
A number of U.S. patents describe solar heat collectors incorporating reflector elements disposed on opposite sides of the absorber element and substantially the entire area of reflector element is pivoted in order to be manually collapsed or folded like a “clam shell” to enclose the absorber element.
U.S. Pat. No. 4,304,218 describes a plurality of elongated solar collectors incorporating compound parabolic reflectors arranged side-by-side within a double glazed window frame. Each solar collector consists of two reflector elements which may be rotated manually from an open reflector position to a closed non-reflector position entirely enclosing the tubular absorber element positioned between the reflector elements themselves. The rotational facility is designed to form a structure resembling a Venetian blind, allowing sunlight into a room interior when the reflector elements are closed.
U.S. Pat. No. 6,363,928 describes a tracking trough collector in which the two reflector elements, after manual removal of a support structure, can be manually collapsed to encase the absorber element to protect the absorber and reflector from adverse weather conditions.
U.S. Pat. Nos. 2,909,171, 2,998,002, 4,196,721, 4,281,644, 4,442,828 and 6,637,428 are examples of small portable collectors with manual folding facility for the reflector elements for ease of transport or to protect the reflector and absorber element from damage when not in use.
None of the collectors with rotatable reflector elements are designed specifically to avoid overheating of the absorber element and require manual intervention to enclose the absorber element. Moreover, the known collector devices utilize rotation of substantially the entire area of reflector elements, that results in a complex drive mechanism and that is non-efficient in avoiding overheating of the absorber element.
More particularly, in the case of non-portable collectors it is not possible to incorporate in an efficient way a drive mechanism for reflector elements having a large and elongated shape due to the relatively large force and energy required to quickly move the entire area of reflector elements that have considerable length and weight.
The document WO 2008/000282 discloses a protective device for a solar panel connector, comprising at least one transparent wall, at least one protective element for covering and protecting the transparent wall, and means for automatically moving the protective element between a first operative position, in which the protective element does not interfere with the transparent wall, and a second operative position, in which the protective element is positioned over, and covers the transparent wall protecting it from bad meteorological conditions and damages.
This device however is also susceptible of improvements.
So, the structure of the non-tracking solar collector devices already known and the conformation of their reflector elements doesn't efficiently prevent overheating of the absorber element disposed between the reflector elements themselves.